Many industrial processes require a reliable source of process gases for a wide variety of applications. Often these gases are stored in cylinders or vessels and then delivered to the process under controlled conditions from the cylinder. For example, the silicon semiconductor manufacturing industry, as well as the compound semiconductor industry, uses a number of hazardous specialty gases such as diborane, stibene, phosphine, arsine, boron trifluoride, hydrogen chloride, and tetrafluoromethane for doping, etching, thin-film deposition, and cleaning. These gases pose significant safety and environmental challenges due to their high toxicity and reactivity. Additionally, storage of hazardous gases under high pressure in metal cylinders is often unacceptable because of the possibility of developing a leak or catastrophic rupture of the cylinder, cylinder valve, or downstream component.
In order to mitigate some of these safety issues associated with high pressure cylinders, there is a need for a low pressure storage and delivery system. Additionally, some gases, such as diborane, tend to decompose when stored for a period of time. Thus, it would be useful to have a way to store unstable gases in a manner that reduces or eliminates the decomposition.
It is also desirable to have a method of removing impurities from gases, particularly in the semiconductor industry. The growth of high quality thin film electronic and optoelectronic cells by chemical vapor deposition or other vapor-based techniques is inhibited by a variety of low-level process impurities which are present in gas streams involved in semiconductor manufacturing or are contributed from various components such as piping, valves, mass flow controllers, filters, and similar components. These impurities can cause defects that reduce yields by increasing the number of rejects, which can be very expensive.
Chemical impurities may originate in the production of the source gas itself, as well as in its subsequent packaging, shipment, storage, handling, and gas distribution system. Although source gas manufacturers typically provide analyses of source gas materials delivered to the semiconductor manufacturing facility, the purity of the gases may change because of leakage into or outgassing of the containers, e.g. gas cylinders, in which the gases are packaged. Impurity contamination may also result from improper gas cylinder changes, leaks into downstream processing equipment, or outgassing of such downstream equipment. Source gases may include impurities, or impurities may occur as a result of decomposition of the stored gases. Furthermore, the impurity levels within the gas container may increase with length of storage time and can also change as the container is consumed by the end user. Thus, there remains a need to be able to remove contaminants from gases, particularly to very low levels.